The objective of this research is to determine whether significant advantages can be achieved in internal fixation of diaphyseal fractures through the use of internal fixation devices of improved design. We wish to test a hypothesis that internal fixation plates and rods of reduced bending, axial and torsional stiffness are superior with respect to the late complication of stress protection induced osteopenia usually observed with traditional management. We have shown advantages to exist with respect to biomechanical properties of canine femora internally fixed with a plate reduced in bending stiffness by a factor of 10. These results were confirmed by quantitative histological measurements. We will expand on these results by testing the intermediate range of bending stiffness values between traditional plate and the extreme case chosen previously in our laboratory (i.e., 1X to 0.1X) to find those optimum values of bending, axial and torsional stiffness which produce both adequate fixation with respect to accomplishment of fracture healing and at the same time minimize the osteopenia response induced by traditional fixation devices. Techniques to be used in this study include periodic x-rays to evaluate fracture healing in the plated canine femoral midshaft osteotomies. Non-destructive and destructive bioengineering tests, quantitative histological measurements using UV light microscopy to evaluate tetracycline labeling, and microradiography will be used to evaluate the influence of the different internal fixation devices employed.